1. Field of the Invention
The present invention relates to a method and apparatus for adjusting the alignment of components on an optical axis in a scattering type particle size distribution measuring equipment by irradiating a diffracting target member with light from a light source, directing the scattered light in such event into a photo-detector via a condenser lens, and measuring the scattered light intensity patterns projected at a specific predetermined location in the photo-detector.
2. Description of the Prior Art
The determination of particle sizes in a sample by their scattering of light is well known in the prior art. FIG. 4 shows a principal portion of a general scattering type particle size distribution measuring equipment, in which numeral 1 denotes a laser tube emitting laser beam 2, numeral 3 is a beam expander for expanding a laser beam 2 as required, numeral 4 is a sample cell for storing the sample 5, numeral 6 is a beam condenser lens mounted behind the cell 4, numeral 7 is a photo detector comprising photo diodes for detecting scattered light from the light condenser lens 6, numeral 8 is a multiplexer for taking in signals from the photo detector 7, and numeral 9 is a CPU to which signals are entered from the multiplexer 8 and which carries out computations based on the scattered light intensity patterns to determine the particle size distribution.
In the scattering type particle size distribution measuring equipment, storing the sample 5 in the cell 4 and irradiating the sample cell 4 with the laser beam 2 causes part of the laser beam 2 to irradiate particles in the sample 5 inside the cell 4 and to become scattered light 10, and the remainder of light passes between particles and becomes transmitted light 11. Both scattered light 10 and transmitted light 11 reach the photo detector 7 via the light condenser lens 6.
Now, in such a scattering type particle size distribution measuring equipment, the optical axis of the laser tube 1 of the light source must strictly coincide with that of the photo detector 7, but if the laser tube 1 is subject to thermal stress, or a bench (not illustrated) equipped with the cell 4, lens 6, photo detector 7, etc. is distorted by heat, or the cell 4 is exchanged, the optical axis location is sometimes changed and deviation occurs.
Therefore, in the conventional scattering type particle size distribution measuring equipment, on the center portion 7A of the optical axis of the photo detector 7, for example, a 4 part-split type light receiving portion 12 for adjusting the optical axis comprising photo diodes is mounted as shown in FIG. 5, and the position of the photo detector 7 is adjusted in such a manner to obtain an equal magnitude of the intensity signals outputted from the four light receiving elements, 12a-12d, respectively, which constitute the light receiving portion 12 for optical axis adjustment to, thereby adjusting the optical axis.
In FIG. 5, numeral 7 denotes a measuring portion for detecting scattered light comprising a plurality of scattered light receiving elements 13a, 13b, 13c, . . . 13n, which are concentrically mounted within the light receiving portion for optical axis adjustment 12 as a center and numeral 14 are isolation gaps provided between the scattered light receiving elements 13a-13n.
In order to carry out an optical axis adjustment as described above, the light receiving portion for optical axis adjustment 12 must be designed to have a radius equivalent to or greater than the size of the variation of a laser beam emitted from the laser tube 1, and if the laser beam varies, for example, by 100 .mu.m at maximum, a 100-.mu.m-in-radius light receiving portion for optical axis adjustment 12 is required for measuring the variation.
Now, in a scattering type particle size distribution equipment, because the greater the diameter of the particle, the smaller is the angle made with the optical axis of the scattered light, it is necessary to form a measuring portion for scattered light detection 13 at a position close to the optical axis center portion 7A, but if a significant size of the light receiving portion for optical axis adjustment 12 is provided as described above, it is unable to provide the scattered light receiving element 13a, etc., in the vicinity of the optical axis center portion 7A, and consequently, a certain limitation has been generated in measuring large-size particles.
Thus the prior art is still seeking an improvement in the operation of a light scattering particle distribution measuring equipment